1. Field of the Invention
The invention relates to the field of closing caps for receptacles or bottles or outer closing for receptacles or bottles previously closed by a cork, a stopper or any other closing means.
More particularly, the invention relates to the field of caps with a heat shrinkable skirt, in other words caps formed from a thermoplastic material that are shrunk onto the neck during crowning by the input of thermal energy, unlike metallic outer closing caps for which the skirt is crimped under the locking ring of the neck during crowning.
More specifically, the invention relates to a new method for the production of caps with a heat shrinkable skirt, outer closing caps and possibly closing caps with a heat shrinkable skirt.
2. Description of Related Art
Heat shrinkable (HS for short) caps have been known for a long time.
Thus, patent FR 805.771 describes the production of a PVC based cap formed by extrusion of a PVC based tube, and then after elongation, expansion of the tube at the exit from the extruder, cooling and cutting of cylindrical tubes into portions forming a heat shrinkable sleeve on the neck of a bottle.
Patent GB 1 105 713 also describes a method for the production of HS caps in which a tube made of a PVC or PS based material is made heat shrinkable by expansion and is flattened and heat sealed transversely at one end so as to close it, and cut off so as to form a flattened cap which, after separation, forms a cap with a welded head that can be placed and heat-shrunk onto a bottle neck.
Patent FR 1 372 805 also describes a method for the production of heat shrinkable tubular sleeves that can be used to seal bottle caps in which a tube is co-extruded in two different types of PE (one relatively meltable and one relatively non-meltable), then cross-linked by irradiation and then expanded.
Patent FR 1 424 731 also describes a method for the production of HS caps in which a portion of a heat shrinkable tube is shrunk onto a template above which a disk is mounted so as to form a heat shrinkable cap for which the head is formed by the disk.
Patent FR 1 441 623 describes a method for the production of a heat shrinkable casing by extrusion of PE, followed by cross-linking by irradiation, and then expansion of the casing.
Patent FR 2 115 137 also describes a method for the production of HS caps in which a blank is formed by cutting it out from a heat shrinkable plastic sheet, and in which a rolled HS cap is formed by welding the side edges by substantially axial overlap. A cap head can also be glued. This cap can be combined with a bottle cork.
Patent FR 2 201 957 also describes a method for the production of HS caps in which a sleeve formed from an extruded tube made of a heat shrinkable and expanded material, is shrunk onto a tapered mandrel on the head of which a stopper made of a heat-formable but non heat shrinkable material is placed.
Patent FR 2 219 080 also describes a HS cap formed on a mandrel by heat shrinkage starting from a PVC or PS tubular part, the end forming the head of the cap being obtained by compaction and compression of a portion with length equal to the length of the tubular part.
U.S. Pat. No. 5 118 460 describes a method for the production of HS caps by moulding. Similarly, patent FR 2 708 513 describes a method for the production of HS caps in which a preform is formed firstly by moulding and is then expanded afterwards.
French patent FR 2 817 193 on behalf of the applicant also describes a method for the production of HS caps that uses an irradiation means.
Known caps or caps with heat shrinkable skirts, and particularly those described in French patent FR 2 817 193, have several disadvantages:                firstly, they make use of an irradiation device that has an investment cost and an operating cost. Furthermore, even if technically the caps thus manufactured do not introduce any risk for the user, some users will be reticent due to the association of “irradiation” and drink packaging means, even if this is unjustified,        secondly, it has been observed that there are dimensional stability problems in the axial direction with caps once they have been heat shrunk onto necks, and since these caps are typically printed, these deformations modify the printing,        furthermore, the hourly productivity of the method has been found to be too low,        finally, the known method does not have sufficient flexibility to satisfy the diversity of new needs, both concerning sensorial properties of caps such as textures, feel or sonority during use or contact, in particular so as to obtain sensorial properties close to various caps considered as being top of the range on the market.        
All these caps also need to be easily opened—without the cap necessarily being provided with easy opening means, either by cutting the top part of the cap with a knife or by “peeling” the cap with a knife from the bottom of the cap depending on habits in each country, being done so without any risk of injury.